The present invention relates to a process for measuring the characteristic dimensions of a spacer or analog used in particular during the manufacturing of some integrated circuits.
The invention especially applies to the field of integrated circuits where it is useful in quality control operations during the manufacturing.
While manufacturing integrated circuits, it may be necessary to constitute specific structures called "spacers".
A spacer is formed by a residue of a given material, exclusively located against the vertical lateral edges of the structures present at the step of the spacer manufacturing.
In order to form spacers, a layer of a given material having a uniform thickness is deposited on the wafer being manufactured, then this layer is anisotropically etched. The etching operation of this layer is stopped as soon as the areas thereof placed on the horizontal or oblique portions of the underlying structures are entirely removed. Under those conditions, the portions of this layer located against the vertical lateral edges of the underlying structures are only partially etched and therefore leave locally in place a flange having a very small width which constitutes the spacer. This technique essentially has the advantage to provide self-aligned microstructures, without masking and photoetching operations. Spacers have several applications in microelectronics, in particular during the realization of lightly doped drains, corresponding to the so-called LDD technique, during silicide deposition on drains, sources and gates without shorting between these parts, or in order to attenuate steps for allowing better passage of the overlying layers.
In all cases when spacers are to be formed, it is necessary to control, during manufacturing, the geometric shapes of the spacers and to be able to measure some specific dimensions. These controls are all the more necessary as the technologic operations leading to formation of spacers are difficult to control and are submitted to drifts, particularly due to the fact that the etching operation has to be abruptly interrupted. Should etching be interrupted too early or too late, or should the etching rate be higher or lower than the rate provided for, the resulting spacer no longer exhibits the suitable shape or dimensions.
A known process for controlling the shape and dimensions of spacers consists in breaking a wafer at right angles to spacers and to examine the cross section through an electronic microscope. This method is expensive, time consuming and critical. Moreover, it is destructive. Up to now, no reliable, non-destructive and immediate process is known for controlling spacers.
Thus, an object of the invention is to provide a process that permits measuring the charateristic dimensions of spacers.